Bioretention is an effective best management practice for urban stormwater. This study aims to provide guidance for selecting the best bioretention medium in terms of pollutant removal capacity. Fuzzy set theory was applied with the improved analytic hierarchy process (IAHP) for weight determination, thus forming the fuzzy synthetic evaluation model, to assess the comprehensive efficiencies of certain sand media. This work is the first to use this method to study bioretention. Results demonstrated that the fuzzy synthetic evaluation model was a rational choice for the selection of bioretention media. The studied media were ranked by pollutant removal capacity as follows: Media III > Media V > Media I > Media VI > Media II > Media VII > Media IV. Media I had the best comprehensive removal efficiency and infiltration rate in bioretention. Moreover, the removal rates for Cd2+, Zn2+ and Pb2+ were excellent (>80%), those for Cu2+ and NH+4-N fluctuated from 58.1% to 92.7% and 64.7% to 95.9%, respectively, and those for NO−3-N and TP of the seven media did not show distinct differences.